The unit’s performance has been faulted by nonprofit groups that seek to limit the influence of money in politics. Melanie Sloan, director of the Citizens for Responsibility and Ethics in Washington, said the Justice Department deserved “to get slammed” for what she portrayed as undertaking a risky prosecution against Mr. Edwards that relied upon a novel interpretation of campaign finance laws, even as it shied away from more traditional corruption cases.

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Daniel Richman, a former federal prosecutor who teaches criminal law at Columbia University, said that the mixed record of the public integrity section — from the cases it did not bring to the decision to prosecute Mr. Edwards — cannot be fairly evaluated without taking into account the additional legal challenges that traditional corruption prosecutions now face.